The present invention relates to a canal structure of an electron multiplier, especially for an X-ray image intensifier (amplifiers), having several perforated metal dynodes which emit secondary electrons and between which plate-shaped separating elements of electrically insulating material with an at least largely regular hole pattern are arranged. Such a canal structure is known from DE-OS No. 26 02 863.
Especially for the construction of flat X-ray tube amplifiers, electron multipliers can be used which have a canal structure (see, for instance, "IEEE Transactions on Nuclear Science", vol. NS-25, no. 2, 1978, pages 964 to 973). Similar known structures comprise generally a layer-like design of several perforated metal dynodes which are parallel to each other and between which a plate-shaped separating element of an electrically insulating material with an at least largely regular hole pattern is arranged. The number, diameter and position of the holes in these separator elements are chosen so that, together with corresponding openings in the dynodes, discrete canal-like feedthroughs through the structure are formed. Accordingly, in the canal structure found in the DE-OS mentioned above, the openings of the metal dynodes are nearly concentric with the openings in the adjoining separating layers. While in this known structure, the separator layers fulfill only an insulation function between adjacent dynodes and can therefore be made relatively thin, the dynodes are comparatively thicker since their canal-like openings have curved, for instance, spherical, walls (see the above-mentioned DE-OS) or conical or truncated pyramid-like shape (see for instance. European patent application No. 0 006 267 Al) in order to increase on them the probability of impinging of electrons. Since the dynodes consist of metals with high secondary electron emission or contain surfaces of these metals, a corresponding multiplication of the electrons at each dynode is obtained.
The manufacture of dynodes with appropriately shaped walls is relatively elaborate, however. In addition, there may be the danger of electric charges at the separating elements. Such charges, however, can adversely affect the electron multiplication in the respective canals in such a manner that a uniform multiplication over the entire cross section of the canal structure can no longer be assured directly.